Recombinant MUC1-MBP fusion protein combined with CpG2006 vaccine induces antigen-specific CTL responses through cDC1-mediated cross-priming mainly regulated by type I IFN signaling in mice.

In this study, we explored the initiation and regulation mechanism of antigen-specific CTL responses induced by a novel cancer vaccine containing recombinant human mucin1-maltose-binding protein fusion protein (MUC1-MBP) and CpG2006. First, DC subsets were analyzed by flow cytometry in vivo and in vitro. After vaccination, the proportion and maturation of cDC1s in mouse dLNs were upregulated, and the proportion of cDC2s and pDCs was also increased. In vitro studies on vaccine components showed similar changs, which may mainly depend on the activity of CpG2006. Subsequently, the regulatory effect of type Ⅰ IFN signaling on CTL triggering was confirmed through co-culture of sorted DC subsets and T cells and subsequent CTL activity experiments. CTL killing activity exhibited a 61.9% decrease once type I IFN signaling was blocked. Further analysis showed that blocking IFNAR1 on cDC1s but not on CTLs resulted in significant defects in CTL killing activity. Collectively, M-M combined with CpG2006 vaccine promotes MUC1-specific CTL responses by increasing the cDC1 activity in mice, and this is mainly regulated by type Ⅰ IFN signaling in cDC1s.

TRAF6-overexpressing dendritic cells loaded with MUC1 peptide enhance anti-tumor activity in B16-MUC1 melanoma-bearing mice.

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) signaling is a critical positive mechanism for the development, homeostasis and activation of immune cells. We investigated the effect of TRAF6 overexpression on dendritic cells (DCs) maturation. TRAF6-overexpressing DCs had increased expression of costimulatory molecules, major histocompatibility complex (MHC) molecules and IL-12 expression. This indicated that TRAF6 promoted the maturation of DCs and indirectly promoted Th1 activation. The antitumor activities between TRAF6-overexpressing DCs and control DCs were compared by administering DCs pulsed with mucin 1 (MUC1) Ag peptide in a therapeutic human MUC1-overexpressing mouse B16 melanoma cells (B16-MUC1) model. Administration of TRAF6-overexpressing DCs significantly inhibited the growth of B16-MUC1 tumors, accompanied by an increase in MUC1-specific Th1 responses and Tc1 responses, as well as a decrease in Tregs levels. TRAF6 signaling has been found to be involved in DCs maturation and Th1 activation in vitro, as well as therapeutic tumor models in vivo, indicating that TRAF6-overexpressing DCs may be a promising approach for cancer immunotherapy.

Anti-PD1 antibody enhances the anti-tumor efficacy of MUC1-MBP fusion protein vaccine via increasing Th1, Tc1 activity and decreasing the proportion of MDSC in the B16-MUC1 melanoma mouse model.

In previous studies, we have obtained a notable anti-tumor efficacy of the recombinant MUC1-MBP vaccine in the process of mouse B16-MUC1 melanoma treatment. However, the tumor cannot be eliminated completely. We found that the tumor inhibition rate decreased from 81.67% (five immunizations) to 43.67% (eight immunizations) after more than five immunizations, indicating persistent vaccine stimulation may activate immunosuppressive factors. In the present study, we revealed that programmed cell death 1 (PD1), an inhibitory molecule suppressing T cell function, expressed on splenic and tumor-infiltrating T cells were up-regulated by the vaccine. Therefore, to optimize the anti-tumor efficacy of the vaccine, we employed combination immunotherapy with MUC1-MBP vaccine and αPD1 (anti-PD1 antibody). Results showed that combination immunotherapy induced a more remarkable anti-tumor efficacy, the tumor clearance being increased to 80% from 20% which obtain by MUC1-MBP vaccine immunizations. To investigate the possible underlying mechanism, IFN-γ secretion and cytotoxic T lymphocyte (CTL) cytotoxicity were measured by enzyme-linked immunosorbent assay (ELISA) and xCELLigence real-time cell analyzer (RTCA) respectively. T cell subsets and immunosuppressive cells in the mouse spleen and tumor microenvironment were analyzed by FACS. Results showed that the proportion of splenic CD8+T cells and tumor infiltration was increased and the activity of CTL killing, T helper 1 (Th1), Type 1 CD8+T (Tc1) was enhanced, indicating that the anti-tumor efficacy enhanced by combination immunotherapy was mainly through boosting CD8+T cells mediated anti-tumor cellular immunity. Additionally, combination immunotherapy significantly decreased the splenic and tumor-infiltrating myeloid derived suppressor cells (MDSCs). These results demonstrated that combination immunotherapy with MUC1-MBP vaccine and αPD1 was capable to invoke a more potent anti-tumor immune response and provide a foundation for further research.